How to calculate front-end debt-to-income ratio, step by step
To calculate your front-end debt-to-income ratio, take your monthly housing payment, divide it by your gross monthly income, and multiply by 100. A $1,800 housing payment on $7,500 a month of gross income is 24.00%. Then do the same for the back-end ratio: add your other monthly debts to the housing payment, divide by the same income, and multiply by 100. Here that is $2,450 of total debt on $7,500 a month, which is 32.67%. The whole method is six steps.
The worked example: $7,500 a month, $1,800 housing, $650 other debts
Step 1 — gross monthly income: $7,500, the pay before tax and benefit withholding, not take-home pay. Step 2 — housing payment: $1,800, the full monthly cost of the home — principal, interest, property tax, homeowners insurance and HOA dues — and the proposed payment, if you are buying. Step 3 — divide the housing by the income and multiply by 100: $1,800 divided by $7,500 is 24.00%, the front-end ratio. Step 4 — other monthly debts: $650. Step 5 — add them to the housing: $1,800 plus $650 is $2,450, the total debt. Step 6 — divide the total debt by the income and multiply by 100: $2,450 divided by $7,500 is 32.67%, the back-end ratio. The debt-to-income-calculator does the same six steps for any income and any debts, with the branches that show what changes when any one of them moves.
What counts as housing
The housing payment is everything the home costs each month, not just the mortgage. Principal and interest are the loan itself; property tax is the monthly share of the yearly bill; homeowners insurance is the premium, monthly; HOA dues are the association fee; and mortgage insurance counts too, if you pay it. On these numbers the whole lot comes to $1,800 a month. If you are buying, use the proposed payment — the one on the house you want. What does not count as housing: utilities, groceries, or repairs. They are real expenses, but lenders leave them out of both ratios — which is why qualifying for a payment and affording it comfortably are not the same thing.
What counts as other debts
The other debts are the required monthly payments on everything that is not the house: car loans, student loans, credit-card minimum payments, personal loans, and court-ordered payments like child support and alimony. Here they come to $650 a month. A deferred student loan still counts — lenders estimate a payment for it. A credit card counts at its minimum payment, not its balance, so a card with a big balance and a small minimum barely moves the ratio while a small loan with a big payment moves it a lot. What does not count: utilities, groceries, subscriptions, or insurance premiums other than the homeowners insurance inside the housing payment. The test is simple: if you must pay it every month or face a default, it counts; if you can skip it, it does not.
The 28/36 rule, and what it means
The classic guideline is the 28/36 rule: keep the front-end ratio at or under 28% and the back-end ratio at or under 36%. On these numbers both hold — 24.00% against the 28% line, 32.67% against the 36% line. The rule is a guideline, not a legal cutoff. Lenders regularly approve loans above 36% back-end with compensating factors — strong credit, cash reserves, a bigger down payment — and conventional underwriting typically stretches to 45% and up to 50%. The 43% figure you will see quoted is the former Qualified Mortgage cap: the CFPB replaced it with a price-based test in July 2021. But 43% is still the number lenders quote — FHA loans use 43% as their standard back-end limit — so treat 36% as the comfort line, 43% as the usual ceiling, and anything above 43% as stretched.
How to work backwards from the lines
To find the income a back-end ratio needs, divide the total debt by the ratio: for a 36% back-end ratio with $2,450 of monthly debt, the income has to be about $6,806 a month — about $81,667 a year. To find the max housing payment at the 28% line, multiply the income by 28%: on $7,500 a month that is about $2,100. To find the max other debt at the 36% line, multiply the income by 36% and subtract the housing: $7,500 times 36% is $2,700, minus $1,800 of housing, is about $900. Those three backwards numbers are the ones that matter before a house hunt: the income you need, the payment you can carry, and the other debts you can still afford.
What counts as a good front-end ratio
There is no single good front-end ratio, because the front end is only half the picture. A 24.00% front end with a 32.67% back end is comfortable; the same 24.00% front end with a 40.83% back end — the same debts on $6,000 a month of income instead of $7,500 — is past the 36% line and inside the 43% ceiling. The honest test is both ratios together: the front end under 28% and the back end under 36% is the zone where a payment is genuinely manageable. A front end over 28% is not a refusal by itself — lenders approve above it every day. If the front end is the tight one, the house is too expensive; if the back end is the tight one, the other debts are.
Common mistakes
The first mistake is dividing by take-home pay: the ratios use gross income, before tax and withholding, because that is what lenders use. The second is leaving a debt out: a deferred student loan, a minimum payment on a card you never carry, a court-ordered payment — the lender finds them all. The third is counting the wrong housing: the mortgage principal and interest alone is not the payment — tax, insurance, HOA dues and mortgage insurance all sit inside it, and leaving them out understates the front end by hundreds a month. The fourth is using the current payment when you are buying: the ratio judges the proposed payment on the house you want, not the rent you pay now. And the fifth is trusting the ratio alone: it says nothing about the credit score, the down payment, or the cash reserves.
A quick check you can do in your head
You can sanity-check any DTI without a calculator. First, the pieces must add up: $1,800 plus $650 is $2,450, and $2,450 divided by $7,500 is 32.67%. Second, the ratios must move the right way: a $6,000 income gives a 30.00% front end and a 40.83% back end, a $9,000 income gives 20.00% and 27.22%, and $1,200 of other debts gives 24.00% and 40.00%. Third, the backwards figures must line up: about $6,806 of income, about $2,100 of housing, and about $900 of other debts all describe the same borrower from three directions. If a DTI breaks any of these checks, the number is wrong — check your numbers in the debt-to-income-calculator against the worked example above.